Aetna CEO: Obamacare In A 'Death Spiral' Heading Into 2018. Aetna and Humana have called off their deal amid government concerns over competition. Here's a look back at six pivotal moments that led to this. Aetna and Humana have called off their deal amid government concerns over competition.
For the plant genus, see Synapsis (plant). Synapsis (also called syndesis) is the pairing of two homologous chromosomes that occurs during meiosis. It allows matching-up of homologous pairs prior to their segregation, and possible chromosomal crossover between them. Synapsis takes place during prophase I of meiosis.
The sequence of events at a synapse is as follows : 1) A nerve impulse reaches the axon terminal of a presynaptic neuron; the membrane is depolarised by an action potential. 2) Depolarisation of the axon terminal during the action potential causes voltage sensitive calcium ion channels to open in the terminal knob.he sequence of events at a synapse is as follows : 1) A nerve impulse reaches the axon terminal of a presynaptic neuron; the membrane is depolarised by an action potential. 2) Depolarisation of the axon terminal during the action potential causes voltage sensitive calcium ion channels to open in the terminal knob.